The present disclosure is directed towards digital watermarking, and in particular, towards digital watermarking of video data for authentication.
Mobile Video Recording (“MVR”) data is typically collected by fleets of vehicles, such as patrol vehicles operated by law enforcement personnel, who record events involving contact with others during their course of duty. Due to the staggering personnel and logistical costs associated with operating current analog, non-indexing MVR systems, there is an overwhelming need for a computerized digital MVR system that is more effective and less costly to operate. However, deployment of digital MVR systems is hindered by authentication issues relevant to evidentiary requirements in courts of law, for example.
Currently, digital MVR storage may not be a legally acceptable storage medium due to its susceptibility to data alteration. Authentication is required to provide an effective means to safeguard the integrity of MVR content, which is essential for its legal acceptance.
MVR applications impose a set of stringent and conflicting requirements on the watermarking algorithm. Any successful algorithm must balance between the need to survive further compression and the sensitivity to detect intentional content tampering, and between speed for real-time marking and algorithm complexity to make counterfeit nearly impossible.
Robust watermarks are designed to withstand content-altering operations such as feature replacement, and their intended use is to claim ownership of digital content in spite of intentional alteration. They are generally not suitable for authentication, where the goal is to reject ownership in cases of content alteration. Fragile watermarks, which are used mainly for authentication purposes, tolerate none or very little change. Fragile watermarks are of little interest either for MVR authentication because they cannot survive lossy compression, an essential requirement in an MVR application. The kind of watermarks that match the MVR needs the closest are often referred to by some researchers as semi-fragile in order to distinguish them from fragile watermarks that tolerate little or no change.
Some watermarks have been designed specifically for video authentication, while others are applicable only to images. But they generally follow a common design principle, which is to find features that are mostly invariant to compression and then to embed watermark bits in the domain of these features. Many also use error-correcting coding (“ECC”) to increase the safety margin of this invariance assumption.
Unfortunately, there are some performance limitations associated with such prior approaches. Firstly, features invariant to compression may be invariant to certain clever tampering as well. For instance, it has been found that the block averages stay mostly unchanged when video is compressed. Consequently, perturbation caused by compression will not likely alter watermark bits embedded in block averages and hence is not detected. However, any alterations that intentionally preserve block averages will not be detected either. Secondly, a delicate and often difficult balance must be reached between insensitivity to compression and sensitivity to tampering. Once the threshold for invariance is exceeded and thus the watermark extraction fails, there is little specificity about the causes for failure.
Accordingly, what is needed is a semi-fragile authentication system and method that enables the deployment of authenticatable digital MVR systems.